(1) The present invention relates to hydraulic dampers mountable on vehicles or aircraft to damp or alleviate the mechanical vibrations associated therewith.
(2) There has been proposed a hydraulic damper of the gas enclosed type comprising a piston slidably housed in a tube. A piston-rod is fitted to the piston, partitioning the tube into upper and lower chambers, which are filled with oil and which are communicated with each other via a passage provided in the piston-rod. A valve mechanism for generating a damping force in such a hydraulic damper is disclosed, for instance, in Japanese Utility Model Application Laid-open No. 85490/1978. That application proposes an arrangement wherein a leaf valve is disposed between a disk plate slidably installed in a hollow nut. A valve seat is stationarily installed within the hollow nut so as to constitute an expansion-side valve which can also function as a damper, even when the expansion stroke is abrupt (the term "expansion-side damping valve" is herein intended to mean a valve which opens only when the piston-rod moves in the expansion direction, A, relative to the tube). In the proposed hydraulic damper, however, the inside surface of the hollow nut in which the disk plate has to slide must be finished with high precision. Additionally, the disk plate has a tendency to incline and scrape the inside surface of the hollow nut, thereby rendering the damper function unstable. To avoid the above-mentioned difficulties, high precision finishing of the damper parts is demanded as well, increasing the cost of the device.